1. Field of the Invention
The present invention relates to an image recording method, a method for improving quality of multicolored images, an image recording apparatus, an ink set, a recording unit, an image forming method, a method for improving image quality, and a method for forming monotone image.
2. Related Background Art
An ink jet recording method is a method of low noise and no impact in which images are recorded by discharging ink directly onto a recording medium. With this method, reduction of running cost, down sizing of the recording apparatus and colorization of images can be easily achieved since this method does not require complicated apparatus. Accordingly, recording apparatuses such as recorders, copying machines, facsimiles and word processors employing this ink-jet recording method have been put into practice. Also, color ink jet recording apparatuses have been put into practice to form multicolor images by the above ink jet recording technology using black ink and at least one color ink selected from, for example, yellow ink, cyan ink, magenta ink, red ink, green ink and blue ink, so as to form multicolored images. In the color ink-jet recording, black ink is most often used, for example, for recording characters, so that sharpness, clearness and high optical density are required for recording with black ink. One known means to satisfy such requirements is to reduce the penetrability of black ink into the recording medium to control the penetration of the coloring material in the black ink into the recording medium.
On the other hand, when two different color inks are fed to a recording medium in a contiguous manner, they may be mixed at the boundary between them to deteriorate the quality of the color image. This phenomenon is called bleeding. To prevent bleeding, there is known a technique to increase the penetrability of color ink into recording media so that different color inks are prevented from mixing with each other on the surface of the recording medium (e.g., Japanese Patent Application Laid-Open No. 55-65269).
In the ink jet recording, to shorten the recording time, there have been proposed several processes; the both-way recording method in which recording is performed on both ways (backward and forward) in the principal scan direction (hereinafter referred to as xe2x80x9cboth-way recordingxe2x80x9d) and the one-pass recording in which an image as wide as the recording head length is formed in one scan. The both-way recording can almost half the recording time on a sheet, since there is no idle carriage run returning to the home position without recording. The one-pass recording where an image is formed by one principal scan does not require multiple scanning on the same site of the recording medium, which can drastically reduce the recording time. There is also known a method to reduce the recording time by moving a carriage at a high speed.
To achieve high grade image, there is also a method called multi-pass recording method where an image of the same width as the length of the recording head is formed by more than one scanning in the principal scanning direction. Such a method can diminish the deviation inherent to each head. In this case, where an image is recorded dividing it into plural regions, a set of mask patterns as shown in the FIG. 19 are used for recording. In FIG. 19, the hatched region represents the recording region and non-hatched region represents non-recording region. The recording region is determined by computing the logical product of the recording region in the mask and the actual image region. It is known that unevenness due to each mask is diminished and images of higher quality can be obtained by using a different mask set for each ink, or using masks with offset for each ink.
It is also known that for the one-pass recording there is a method to achieve the same effect as in the multi-pass recording method by using more than one heads for the same ink. FIG. 20 is an example of heads for this method, where the heads 84 containing black ink are provided on either side of the color ink heads 81-83. In this case, the heads on both sides, which eject the same ink, are in a complementary relationship employing the masks as shown in FIG. 19.
After carrying out an investigation from various approaches so as to achieve shorter recording time and higher record quality by the both-way recording method or multi-pass recording or multi-head recording in the color ink-jet recording using black ink of low penetrability and color ink of high penetrability as described above, the present inventors have recognized the following technical problem. In the color ink-jet recording, black ink and color ink may be overlapped each other to achieve more smooth gradation. The present inventors have found that, when such recording is carried out by using an ink-jet recording apparatus capable of both-way recording as described above, or by using different masks for the color head and the black head in multi-pass recording, or by using an ink-jet recording apparatus having two or more heads containing the same ink, the reproduced color tone may vary depending on the recording order of the color ink and the black ink. That is, the reproduced color tone, which must be inherently the same, may vary depending on whether it was recorded by the head scanning in the forward direction or in the backward direction (hereinafter this phenomenon is referred to as xe2x80x9cstreakiness of both-way recordingxe2x80x9d). This streakiness of both-way recording is conspicuous where color ink and black ink were applied at a relatively large amount on the recording medium. Also, when different masks are used for a color head and a black head in multi-pass recording, or when the apparatus has two or more heads containing the same ink, image regions where the application order of black ink and color ink was different from the other region are present, which may lead to irregularity.
This phenomenon (irregularity due to the difference in application order of black ink and color ink) may considerably deteriorate images, in particular, of images in which black ink and color inks are intermingled. The present inventors have come to a conclusion that, in order to develop an ink jet recording apparatus capable of recording multi-color images of higher quality at a higher speed, thiS technical problem must be solved by all means.
Accordingly, one object of the present invention is to provide an image recording method which enables the recording of multi-color images of higher quality in a shorter period of time.
Another object of the present invention is to provide a method of improving the image quality of multi-color images which are produced using an ink jet recording apparatus.
Still another object of the present invention is to provide an image recording apparatus which can record multicolor images of higher quality at a high speed.
A further object of the present invention is to provide an ink set and a recording unit suitably used in an ink jet recording apparatus which enables recording of multicolor images of higher quality at a high speed.
The other object of the invention is to provide a method for obtaining images having visually uniform feeling.
Still the other object of the invention is to provide a method for improving the image grade to obtain images having uniform feeling using an ink-jet recording apparatus.
Still the other object of the present invention is a method for forming monotone image to obtain images expressed in more smooth monotone gradation.
According to one aspect of the present invention, there is provided a method of recording a multi-color image, wherein the multi-color image contains image regions formed by applying an black ink and a color ink to overlap each other in different orders, characterized in that the black ink contains a salt, an aqueous medium and a pigment dispersed in the aqueous medium by the action of an ionic group, and the color ink contains a dye.
According to one aspect of the present invention, there is provided a method of improving the image quality of an multi-color image by using an ink-jet recording head separately containing a black ink and a color ink, the multi-color image containing a plurality of image regions formed by applying an black ink and a color ink to overlap each other in different orders, characterized in that the black ink contains a salt, an aqueous medium and a pigment dispersed in the aqueous medium by the action of an ionic group, and the color ink contains a dye.
According to one aspect of the present invention, there is provided an image recording apparatus comprising:
(i) an ink jet recording head from which a black ink and a color ink are discharged separately at a recording medium; and
(ii) means for carrying a recording medium to a position where the recording head carry out recording; characterized in that the black ink contains a salt, an aqueous medium and a pigment dispersed in the aqueous medium by the action of an ionic group, and the color ink contains a dye.
According to one aspect of the present invention, there is provided an ink set comprising a combination of a black ink and a color ink, the black ink containing a salt, an aqueous medium and a pigment dispersed in the aqueous medium by the action of an ionic group, the color ink containing a component which destabilizes the dispersion stability of the pigment of the black ink when the color ink and the black ink are mixed, the component being a dye, an additive, or a dye and an additive.
According to one aspect of the present invention, there is provided a recording unit comprising a black ink holding part which holds an black ink, a first ink jet head from which the black ink is discharged, a color ink holding part which holds a color ink and a second ink jet head from which the color ink is discharged, the black ink containing a salt, an aqueous medium and a pigment dispersed in the aqueous medium by the action of an ionic group, the color ink containing a component which destabilizes the dispersion stability of the pigment of the black ink when the color ink and the black ink are mixed, the component being a dye, an additive, or a dye and an additive.
According to one aspect of the present invention, there is provided an image forming method comprising the steps of:
(i) forming a first image region by applying a black ink to a recording medium, and
(ii) forming a second image region by applying a black ink and a color ink to overlap each other onto the recording medium;
characterized in that the black ink comprises a salt, an aqueous medium, and a pigment dispersed in the aqueous medium by the action of an ionic group, and at least one color ink contains a dye or an additive or both, the dye and the additive destabilizing the dispersion stability of the pigment when mixed with the black ink.
According to one aspect of the present invention, there is provided a method for improving quality of a black image being formed by forming a first black image by applying a black ink to a recording medium, and forming a second black image by applying a black ink and a color ink to overlap each other onto the recording medium, characterized in that the black ink comprises a salt, an aqueous medium and a pigment dispersed in the aqueous medium by the action of an ionic group, and the color ink contains a dye or an additive or both where the dye and the additive destabilize the dispersion stability of the pigment when mixed with the black ink.
According to one aspect of the present invention, there is provided a method for forming a monotone image characterized in that an ink set above mentioned is used.
By employing the above mentioned various constitutions, it is possible to greatly improve the density unevenness in both-way recording which may be observed when, for example, recording of multicolor images is carried out at a high speed recording not only in the outward head scan direction but also in homeward direction. In one-pass both-way recording, it is also possible to obtain an excellent image of which optical density would not vary according to the recording directions. Further, it is possible to suppress the poor uniform feeling of the image formed by the multi-pass recording, which may occur due to the presence of sites where the application order of color ink and black ink is different, to obtain good images.
As a more preferable aspect of the present invention, there is a recording method using color ink containing a dye or an additive or both which destabilizes the dispersion stability of the pigment in black ink when mixed with the black ink. Such a configuration can effectively improve the streakiness of both-way recording or uniform feeling of images recorded by the multi-pass recording.